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"I have got no cartilage in my knee, so every time I jump it is just bone on bone; it just bruises, releases fluid," Dagg said.

"It would be alright if I just had to trundle around, but I have got to be explosive. But I am through it now, I am on the other side. I have just got to keep positive and deal with the new normal. I am not my old self, but I can still play footy. That is the main thing.

"Hopefully that (stem cell treatment) works, and apparently it regenerates cartilage and that is what I need. I need cartilage in between my bones, because pretty much it is just bone on bone."

He has to ensure that the way he runs doesn't aggravate the problem.

Dagg said: "It is like starting to walk again. You have got to train yourself to use the same power out of each leg and things like that. It was a bit of a learning curve but I am just happy to be throwing the ball around again."

Nadal is among the sports people who have used stem cell therapy - the Spaniard had fat and bone marrow cells injected to treat his back issues in 2014. He has since risen back to the top of world tennis.

Even the 82-year-old Indianapolis 5000 legend A.J.Foyt had the therapy, on ankle and shoulder problems. But the procedure is considered so alternative that NFL teams for instance don't pay the medical costs, according to one Sports Illustrated report three years ago.

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